Bryozoa (moss animals, sea mats, polyzoa, corallines, and ectoprocts)

Introduction

Bryozoa are also known as moss animals, sea mats, polyzoa, corallines and ectoprocts. They usually occur in colonies in the shallows, and are often mistaken for algae or sponges. There are about 4300 described species, and they have no fossil record until the Ordovician.

Bryozoa body plan

Individuals are minute, usually measuring less than 0.5 mm long (see Bowerbankia sp). right. Some species are erect, branched or lobes, whilst others are flat and moss-like. The lophophore (see left which shows the lophophore from the side and above) can be retracted when the animal is disturbed. The tentacles are covered with cilia, the beating of which sets up a water current to collect food particles. The particles are then passed down the cilia to the mouth. A freshwater bryozoan colony can be up to 5 cm long.

The eggs or statoblasts of some freshwater species can withstand freezing and desiccation, and usually germinate in the spring.

They are usually found in clear ponds and lakes on the undersides of water-lily leaves or the upper surfaces of stones, weed and shells. A colony can move about 10 cm a day, and can extent for over a metre.

On the left are some individuals of Crisatella mucedo a freshwater bryozoan. A Cristatella mucedo colony looks like a piece of furry jelly. It is found in clear ponds and lakes on the upper surface of plants and stones over which it creeps. It prefers exposure to the light. Its colonies can somtimes divide in 2 through the middle. It is also possible for 2 colonies to fues together into one.

On the left is Adeona sp., so found in Australian waters.

Below is a fossilized Chasmatopora furcata, a bryozoan from the early Ordovician, about 450 million years ago, found in what is now Estonia.